全文获取类型
收费全文 | 2498篇 |
免费 | 233篇 |
国内免费 | 1篇 |
专业分类
2732篇 |
出版年
2021年 | 20篇 |
2020年 | 18篇 |
2018年 | 22篇 |
2017年 | 22篇 |
2016年 | 46篇 |
2015年 | 88篇 |
2014年 | 112篇 |
2013年 | 100篇 |
2012年 | 132篇 |
2011年 | 108篇 |
2010年 | 94篇 |
2009年 | 67篇 |
2008年 | 116篇 |
2007年 | 96篇 |
2006年 | 112篇 |
2005年 | 98篇 |
2004年 | 92篇 |
2003年 | 104篇 |
2002年 | 82篇 |
2001年 | 61篇 |
2000年 | 71篇 |
1999年 | 64篇 |
1998年 | 22篇 |
1997年 | 30篇 |
1996年 | 35篇 |
1995年 | 19篇 |
1994年 | 23篇 |
1993年 | 24篇 |
1992年 | 42篇 |
1991年 | 47篇 |
1990年 | 51篇 |
1989年 | 45篇 |
1988年 | 30篇 |
1987年 | 36篇 |
1986年 | 29篇 |
1985年 | 25篇 |
1984年 | 31篇 |
1983年 | 32篇 |
1982年 | 23篇 |
1981年 | 18篇 |
1980年 | 20篇 |
1979年 | 29篇 |
1978年 | 35篇 |
1977年 | 23篇 |
1976年 | 24篇 |
1975年 | 23篇 |
1974年 | 40篇 |
1973年 | 19篇 |
1972年 | 23篇 |
1970年 | 20篇 |
排序方式: 共有2732条查询结果,搜索用时 15 毫秒
21.
Aortic accumulation and plasma clearance of beta-VLDL and HDL: effects of diet-induced hypercholesterolemia in rabbits 总被引:6,自引:0,他引:6
To assess the role of beta-VLDL in diet-induced atherogenesis, the in vivo metabolism and aortic accumulation of 125I-labeled beta-VLDL were investigated in cholesterol-fed rabbits and chow-fed controls. 125I-labeled HDL and 125I-labeled albumin were studied for comparison. The fractional catabolic rate of 125I-labeled beta-VLDL was reduced in cholesterol-fed rabbits (0.011 vs 0.139 hr-1), but due to the high endogenous pool, the total beta-VLDL flux was very high (13.1 vs less than 1.1 mg/kg per 24 hr). These results suggest that elevated levels of beta-VLDL during cholesterol feeding were due to an enhanced rate of synthesis, a finding confirmed in hypercholesterolemic rabbits subjected to plasmapheresis. Following acute reduction of plasma cholesterol by plasmapheresis, the quantitative increases in beta-VLDL cholesterol concentrations (210 to 364 mg/dl) over the subsequent 24 hr were in agreement with the rise calculated from the plasma clearance kinetics of 125I-labeled beta-VLDL (378 mg/dl per 24 hr). Aortic accumulation of beta-VLDL in hypercholesterolemic rabbits was increased greater than 15-fold over controls. Accumulation was predominantly in the intimal atheromatous lesions. The fractional catabolic rate of 125I-labeled HDL was increased during cholesterol feeding (0.037 vs 0.021 hr-1). A decreased rate of synthesis appeared to be responsible for the markedly depleted plasma HDL. HDL accumulation within the aorta was attenuated greater than 9-fold in cholesterol-fed rabbits compared to those fed normal chow. Plasma kinetics and aortic accumulation of 125I-labeled albumin were similar in hypercholesterolemic and control rabbits.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
22.
23.
Approximate case influence for the proportional hazards regression model with censored data 总被引:2,自引:0,他引:2
A method is presented for approximating the influence of individual cases upon regression coefficient estimates obtained from the Cox proportional hazards model. Observations can thus be identified which may greatly influence statistical inferences regarding the effects of prognostic factors upon survival time. An example from a cancer clinical trial is given. 相似文献
24.
Two models for a maternal factor in the inheritance of Huntington disease 总被引:12,自引:8,他引:4 下载免费PDF全文
Huntington disease is a classic example of an autosomal dominant trait. Over the years, however, a number of investigators have reported anomalies regarding the age of onset of the disease that are inconsistent with this paradigm. We propose two models in which a maternal factor--cytoplasmic in one case, autosomal or X-linked in the other--acts to delay onset in a manner consistent with the previously reported anomalies. Relevant data from the Huntington's Disease Research Roster are presented that reinforce and extend the previous observations. 相似文献
25.
Activation of the gene coding for variant surface glycoprotein (VSG) 118 in Trypanosoma brucei proceeds via a duplicative transposition to a telomeric expression site. The resulting active expression-linked extra copy (ELC) is usually flanked by DNA that lacks sites for most restriction enzymes and that is thought to interfere with the cloning of the ELC as recombinant DNA in Escherichia coli. We have circumvented this problem by cloning an aberrant 118 ELC gene, flanked at the 3'-side by at least 1 kb DNA, that contains restriction enzyme sites. Our analysis shows that this DNA and the 3'-end of the 118 ELC gene are derived from another VSG gene (1.1006) that is permanently located at a telomeric position. We propose that the 3'-end of the 1.1006 gene and (all of) its 3' flanking sequence moved to the expression site by a telomere conversion. Such a telomere conversion can also account for the appearance of an extra copy of the 1.1006 gene detected in a sub-population of our trypanosome strain. 相似文献
26.
27.
Prof. Dr. W. Lange 《Cell and tissue research》1974,153(2):219-226
Summary The number of Golgi cells per unit volume was determined in different regions of the cerebellar cortex of man and of ten other mammals. Despite the general belief in the uniform architecture of the cerebellar cortex, regional differences in the distribution of Golgi cells were found. In the inferior parts of the vermis, the number of Golgi cells per unit volume is twice that in the corresponding hemispheres. In addition, there are differences between the anterior and inferior parts of the vermis. These differences are a feature of the cytoarchitecture of the cerebellum in man and all the investigated mammals. The ratio of Purkinje cells to Golgi cells was also determined and found to differ in different species. In man, this ratio is 11.5, while in the monkey and cat it is almost 11.9 and in the rat 13.3. These differences in the ratio of Purkinje cells to Golgi cells are discussed from the point of view of cerebellar evolution.Supported by the Deutsche Forschungsgemeinschaft. 相似文献
28.
The monomers γ-benzylglutamyl-ε-benzyloxycarbonyl-lysylalanylglycine pentachlorophenyl ester and alanyl-γ-benzyl-D -glutamyl-ε-benzyloxycarbonyllysyl-D -alanyl-glycine pentachlorophenyl ester, were polymerized in dilute solutions of dimethylform-amide (DMF) or as dispersions in the same volume of benzene. After deprotection with hydrogen bromide, the products were either chromatographed on Sephadex G-50 or dialyzed. The polymers derived from the polymerization in benzene were considerably larger than those from DMF. The results in benzene indicated that high monomer to solvent ratios are not necessary for the production of high-molecular-weight sequential polypeptides. Circular dichroism spectra of the polymers and monomers at neutral and acid pH indicated that poly(L -Glu-L -Lys-L -Ala-Gly) exists in a random coil configuration and poly(L -Ala-D -Glu-L -Lys-D -Ala-Gly) exists in a β conformation. 相似文献
29.
30.